 For example, "Transformación" (1974) strongly recalls Ligeti’s "Lux aeterna" (1966)—both are composed for 16 solo voices—as well as the harmonic overtone-singing of Stockhausen’s "Stimmung" (1968).In 1965 he began a brief association with the neo-Dada composers’ group Zaj, founded the previous year by Walter Marchetti, Juan Hidalgo, and Ramón Barce .He helped to found the Studio Nueva Generación in 1967 , by which time some of his compositions were beginning to include references to historical styles and quotations from earlier composers—for example, "Angelus novus" (1971) refers to Gustav Mahler, the Cello Concerto (1976) is based on themes by Manuel de Falla as well as the "Cant dels ocells" by Pablo Casals, and his Fourth and Fifth Symphonies (1987 and 1989, respectively) both use a quotation from Richard Strauss's "Also sprach Zarathustra" —and for this reason his name is sometimes connected with the German New Simplicity composers .